Re: Function returns null

*To*: mathgroup at smc.vnet.net*Subject*: [mg104724] Re: Function returns null*From*: Bill Rowe <readnews at sbcglobal.net>*Date*: Sun, 8 Nov 2009 06:42:37 -0500 (EST)

On 11/7/09 at 6:46 AM, mgreene at csumb.edu (Michael Greene) wrote: >I'm getting an unexpected result when I remove a print statement >from my function. The function computes a single digit sum of digits >and returns what I expect as long as the print statement just prior >to the function exit is present. I can verify that by invoking the >function within a print statement, e.g., >Print["sOd returned - ",sOd[3329]] >When I remove the print within the function, the function returns a >null result. What simple point am I missing ? Does the := operator >have something to do with this? >Here is the function: (with embedded print statement) >sOd[x0_] := Module[{sodv, x, digit}, >x = IntegerPart[x0]; (* ensure we have an integer input*) >sodv = x; >If[(x > 9), { (* sum digits if input has two or more digits*) >sodv = 0; >While[x > 0, >digit = (FractionalPart[x /10])*10; >sodv = sodv + digit; >x = IntegerPart[x/10]; >]; >sodv = sOd[sodv]; (* check for multiple digit sum *) >} >] >Print["sOd returns -", sodv]; (* remove this and function returns null*) >Return[sodv]; (* return single digit sum *) >] Module returns the result of the last expression which is Return[sodv];. This is a compound expression equivalent to Return[sodv];Null which is why you get the Null. Change this to Return[sodv] and things will behave as you expected. Also, I note the code is much more complex than need by to compute the sum of digits in an integer. The following code has the same functionality as your code: sOd[x_Integer] := FixedPoint[Total[IntegerDigits@#] &, x]